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    ITEC 1010 Information and Organizations

    Chapter 4

    Linking Info. Tech.

    ITEC 1010 Information and Organizations

    Communications

    Communications

    The message (data and information) is

    communicated via the signal

    The transmission medium carries the signal

    Sender ReceiverSignal

    Transmissionmedium

    ITEC 1010 Information and Organizations

    Communications Discussion

    The transmission of data from one computer to another, orfrom one device to another. A communications device,

    therefore, is any machine that assists data transmission. For

    example, modems, cables, and ports are all communications

    devices. Communications software refers to programs that

    make it possible to transmit data.

    ITEC 1010 Information and Organizations

    Telecommunications

    Telecommunications

    The electronic transmission of signals for

    communications, including such means as:

    Telephone

    Radio

    Television

    Telecommunication medium Anything that carries an elec tronic signal and interfaces

    between a sending device and a receiving device

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    ITEC 1010 Information and Organizations

    Communications andTelecommunications

    In human speech, the sender transmits a signal throughthe transmission medium of the air

    In telecommunications, the sender transmits a signalthrough the transmission medium of a cable

    Schematic

    ITEC 1010 Information and Organizations

    ITEC 1010 Information and Organizations

    Data Communications

    Data communications

    A specialized subset of telecommunicationsthat refers to the electronic collection,processing, and distribution of data -- typically

    between computer system hardware devices

    ITEC 1010 Information and Organizations

    Elements of a

    Telecommunications System

    Telecommunication devices

    Relay signals between computer systems andtransmission media

    Schematic

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    ITEC 1010 Information and Organizations ITEC 1010 Information and Organizations

    Computer Network

    Computer network

    The communications media, devices, and

    software needed to connect two or morecomputer systems and/or devices

    Used to share hardware, programs, anddatabases across the organization

    Fosters teamwork, innovative ideas, and new

    business strategies

    ITEC 1010 Information and Organizations

    Speed of Communications BPS

    In telecommunications and computing, bit rate ordata rate is the number of bits that are conveyed or

    processed per unit of time.

    The bit rate is quantified using the 'bits per second'

    (bit/s or bps) unit, often in conjunction with a SI

    prefix such as kilo- (kbit/s or kbps), mega-(Mbit/s or

    Mbps), giga-(Gbit/s or Gbps) or tera (Tbit/s or Tbps).

    ITEC 1010 Information and Organizations

    Types of communications Media

    Twisted pair wire cable Insulated pairs of wires historically used in

    telephone service and to connect computerdevices

    Coaxial cable Consists of an inner conductor wire

    surrounded by insulation, called the dielectric

    The dielectric is surrounded by a conductiveshield, which is surrounded by a non-conductive jacket. Coaxial cable has betterdata transmission ra te than twisted pair

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    ITEC 1010 Information and Organizations

    Types of communications Media

    Fiber-optic Cable Many extremely thin

    strands of glass or plasticbound together in asheathing whichtransmits signals withlight beams

    Can be used for voice,data, and video

    ITEC 1010 Information and Organizations

    Other types ofTelecommunications Media

    Microwave Communications

    Satellite transmission

    Cellular transmission

    Infrared transmission

    Pretty picture

    ITEC 1010 Information and Organizations ITEC 1010 Information and Organizations

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    ITEC 1010 Information and Organizations ITEC 1010 Information and Organizations

    Terminology

    Analog Signal

    A continuous, curving signal

    Digital Signal

    A signal represented by bits

    Modems

    Devices that translate data from digital to

    analog and analog to digital

    ITEC 1010 Information and Organizations

    Analog /Digital

    Almost everything in the world can be described or representedin one of two forms: analog or digital. The principal feature ofanalog representations is that they are continuous. In contrast,digital representations consist of values measured at discreteintervals.

    Digital watches are called digital because they go from onevalue to the next without displaying all intermediate values.Consequently, they can display only a finite number of times of

    the day.

    ITEC 1010 Information and Organizations

    Analog Discussion (1)

    In contrast, watches with hands are analog, because the hands movecontinuously around the clock face. As the minute hand goes

    around, it not only touches the numbers 1 through 12, but also the

    infinite number of points in between.

    Early attempts at building computers used analog techniques, but

    accuracy and reliabili ty were not good enough. Today, almost all

    computers are digital.

    Analog /Digital

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    ITEC 1010 Information and Organizations

    Digital Discussion (1)

    Describes any system based on discontinuous data or events.

    Computers are digital machines because at their most basic levelthey can distinguish between just two values, 0 and 1, or off andon.

    There is no simple way to represent all the values in between, suchas 0.25. All data that a computer processes must be encodeddigitally, as a series of zeroes and ones.

    The opposite of digital is analog. A typical analog device is a clockin which the hands move continuously around the face. Such aclock is capable of indicating every possible time of day. Incontrast, a digital clock is capable of representing only a finitenumber of times (every tenth of a second, for example).

    Analog /Digital

    ITEC 1010 Information and Organizations

    In general, humans experience the world analogically. Vision, forexample, is an analog experience because we perceive infinitelysmooth gradations of shapes and colors.

    Most analog events, however, can be simulated digitally.Photographs in newspapers, for instance, consist of an array ofdots that are either black or white.

    From afar, the viewer does not see the dots (the digital form), butonly lines and shading, which appear to be continuous.

    Although digital representations are approximations of analogevents, they are useful because they are relatively easy to store andmanipulate electronically.

    The trick is in converting from analog to digital, and back again.

    Analog /Digital

    ITEC 1010 Information and Organizations

    This is the principle behind compact discs (CDs). The musicitself exists in an analog form, as waves in the air, but thesesounds are then translated into a digital form that is encodedonto the disk.

    When you play a compact disc, the CD player reads the digitaldata, translates it back into its original analog form, and sends itto the amplifier and eventually the speakers.

    Internally, computers are digital because they consist of discreteunits called bits that are either on or off. But by combining

    many bits in complex ways, computers simulate analog events.

    In one sense, this is what computer science is all about.

    Analog /Digital

    ITEC 1010 Information and Organizations

    How a Modem Works

    Modem

    Modulates a digital signal into an analog signalfor transmission via analog medium, thendemodulates the signal into digital for receiving

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    ITEC 1010 Information and Organizations

    Modem Acronym for modulator-demodulator. A modem is a device that

    enables a computer to transmit data over telephone lines.

    Computer information is stored digitally, whereas informationtransmitted over telephone lines is transmitted in the form ofanalog waves. A modem converts between these two forms.

    Fortunately, there is one standard interface for connecting

    external modems to computers called RS-232. Consequently,

    any external modem can be attached to any computer that hasan RS-232 port, which almost all personal computers have.

    There are also modems that come as an expansion board that

    you can insert into a vacant expansion slot. These are

    sometimes called onboard or internal modems.

    ITEC 1010 Information and Organizations

    Multiplexer

    Multiplexer

    Allows several telecommunications signals to

    be transmitted over a single communicationsmedium at the same time

    ITEC 1010 Information and Organizations

    Carriers and Services (1)

    Carriers Organizations that take the responsibility of ensuring telecommunications

    can effectively take place between enterprises

    Common carriers Long-distance telephone companies

    Value-added carriers Companies that have developed private telecommunications systems and

    offer their services for a fee

    Switched lines Lines that use switching equipment to allow one transmission device to

    be connected to other transmission devices (e.g., standard telephone line)

    Dedicated line A line that provides constant connection between two po ints. No

    switching or dialing is needed

    ITEC 1010 Information and Organizations

    Carriers and Services (2)

    Private branch exchange (PBX)

    Communication system that can manage both voice and data transfer

    within a location (e.g. a building) and to outside lines

    Wide area telecommunication service (WATS)

    Billing method fo r heavy users of voice services

    Phone and dialing services

    Includes automatic number identification (a.k.a. caller ID)

    Integration of telephones and personal computers

    Access code screening

    Call priorities

    One number portability (use anywhere)

    Intelligent dialing (auto re-dial for a busy number)

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    ITEC 1010 Information and Organizations

    ISDN ISDN = Integrated Services Digital Network

    Technology that uses existing common-carrier linesto simultaneously transmit voice, video, and image

    data in digital form

    Pretty picture

    Carriers and Services (3)

    ITEC 1010 Information and Organizations

    ITEC 1010 Information and Organizations

    T1 carriers An expensive service developed by AT&T to

    increase the number of voice calls that could be

    handled through existing cables

    Digital subscriber lines (DSL) Uses existing phone wires going into todays homes

    and businesses to provide transmission speeds

    exceeding 500 Kbps at a cost of $100 - $300 per

    month

    Carriers and Services (4)

    ITEC 1010 Information and Organizations

    Networks and Distributed

    Processing

    Centralized processing Data processing that occurs in a single location or

    facility

    Decentralized processing Data processing that occurs when devices are placed at

    various remote locations

    Distributed processing Data processing that occurs when computers are

    placed at remote locations but are connected to eachother via telecommunications devices

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    ITEC 1010 Information and Organizations

    Network Topology

    Network Topology A logical model that describes how networks

    are structured or configured

    Topologies

    Ring Bus Star Hybrid

    ITEC 1010 Information and Organizations

    Switch/Hub

    Start topology links the computers by individual cables to a

    central unit, usually a hub. When a computer or other

    networking component transmits a signal to the network,

    the signal travels to the hub.

    Then, the hub forwards the signal simultaneously to all

    other components connected to the hub. Ethernet 10BaseTis a network based on the star topology. Star topology is the

    most popular way to connect computers in a workgroup or

    departmental network

    Network Topology

    ITEC 1010 Information and Organizations

    Ring A ring topology connects the computers along a single path

    whose ends are joined to form a circle.

    The ring topology is commonly used in token ring networks

    that the ring of a token ring network is concentrated inside a

    device called a Multistation Access Unit (MAU) and fiber

    Distributed Data Interface (FDDI) networks that the ring in thiscase is both a physical and logical ring and usually runs around

    a campus or collection of buildings to form a high-speed

    backbone network.

    Network Topology

    ITEC 1010 Information and Organizations

    Bus A bus topology connects computers along a single or more

    cable to connect linearly as figure 1. A network that uses a bus

    topology is referred to as a "bus network" which was the

    original form of Ethernet networks. Ethernet 10Base2 (also

    known as thinnet) is used for bus topology

    Network Topology

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    ITEC 1010 Information and Organizations

    Hierarchical Uses treelike structures

    with messages passedalong the branches of the

    hierarchy

    Hybrid Network made up of

    various types oftopologies

    Network Topology

    ITEC 1010 Information and Organizations

    Network Types

    Local area network (LAN) Connects computer systems and devices in the same

    geographic area (can be Ring, Bus, Hierarchical, Star,Hybrid)

    Wide area network (WAN) Ties together large geographic regions using

    microwave and satellite transmission or telephonelines

    VAN Network provide additional services such as games,

    fax, phone etc.

    ITEC 1010 Information and Organizations

    File Server Connection

    Applications and databases reside on the samehost computer

    File server transfers data and programs to PCs

    on the network, where these target PCsperform most of the processing

    Host

    computer

    File downloadedto user

    File server

    Target PC

    ITEC 1010 Information and Organizations

    Client/Server Connection

    Applications and databases reside onspecialized host computers

    Servers do most or all of the processing andtransmit the results to the client

    Client Server

    Server ServerClient

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    ITEC 1010 Information and Organizations

    Adv. & Disadv. of Client/Server

    Advantages Reduced cost potential

    Improved Performance

    Increased Security

    Disadvantages Increased cost potential

    Loss of control

    Complex multi-vendor

    environment

    ITEC 1010 Information and Organizations

    Network Applications

    Linking personal computers to server computers Download and upload information

    Voice mail Enables users to leave, receive, and store verbal

    messages for and from other users

    Electronic mail (e-mail) Enables a sender to connect a computer to a network,

    type messages, and send it to another person on thenetwork

    ITEC 1010 Information and Organizations

    Electronic software distribution Involves installing software on a file server for users to share

    by signing onto the network and requesting that the softwarebe downloaded onto their computers over a network

    Electronic document distribution Transporting documents -- such as sales reports, policy

    manuals, and advertising brochures -- over communications

    lines and networks

    Telecommuting Enables employees to work away from the office using

    personal computers and networks to communicate viaelectronic mail with other workers and to pick up and deliverresults

    Network Applications

    ITEC 1010 Information and Organizations

    Videoconferencing

    Allows participants to conduct long-distancemeetings face to face while eliminating

    Pretty picture

    Network Applications

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    ITEC 1010 Information and Organizations ITEC 1010 Information and Organizations

    Electronic Data Interchange (EDI) Uses network systems and follows standards and

    procedures that allow output from one system to be

    processed directly as input to other systems, withouthuman intervention

    EFT Electronic Fund transfer service sending money online

    to other accounts. To may utility bills, other online

    payments, payment using Credit card.

    Pretty picture

    Network Applications

    ITEC 1010 Information and Organizations

    EDI link

    EDI link EDI link

    Vendor Customer

    Vendor Customer

    Third-partyclearing house

    (a)

    (b)

    ITEC 1010 Information and Organizations

    Public network services

    Services that give personal computer users access to vast

    databases and other services, usually for an initial fee

    plus usage fees

    Specialized and regional information services BBS

    Specialized electronic bulletin boards and e-mail services

    targeting particular interests.

    Distance learning

    Use of telecommunications to extend the classroom

    Network Applications